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  • 1
    Electronic Resource
    Electronic Resource
    Surface impedance of YBa2Cu3O7−x thin film grain boundary Josephson junctions: Evaluation of the IcRn product (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4581-4587 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature and the dc magnetic field dependence of the effective surface impedance Zs of epitaxial YBa2Cu3O7−x thin films on [001] tilt SrTiO3 bicrystals with tilt angles of 36.8° and 24° have been investigated at 87 GHz. The effects of the grain boundaries become increasingly important with decreasing characteristic voltage IcRn and increasing unit areal normal resistance RnA. The boundaries can consistently be described with a resistively shunted Josephson transmission line model taking into account the effect of finite film thickness. Thermal or magnetic loading of the junction leads to additional losses, whereas the effective microwave penetration depth exhibits a specific extremal behavior. From the magnetic response of Zs at 4.2 K, the junction lower critical fields as well as the values of IcRn and RnA can be deduced. The data agree well with dc transport measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355953
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  • 2
    Electronic Resource
    Electronic Resource
    Nonlinear dielectric microwave losses in MgO substrates (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 1007-1009 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the nonlinear surface impedance and two-tone intermodulation distortion of ten epitaxial YBa2Cu3O7−δ films on MgO substrates, using stripline resonators, at frequencies f=2.3–11.2 GHz and temperatures T=1.7 K−TC. The power dissipation decreased by up to one order of magnitude as the microwave electric field was increased to 100 V/m for T〈20 K. The reactance showed only a weak increase. The minimum of the losses correlated with a plateau in the intermodulation signal. The same features were observed for a Nb film on MgO but not for YBa2Cu3O7−δ and Nb on LaAlO3 or sapphire. The anomalous response results from dielectric losses in MgO, most probably due to defect dipole relaxation. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1447000
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  • 3
    Electronic Resource
    Electronic Resource
    Spatially resolved microwave field distribution in YBaCuO disk resonators visualized by laser scanning (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3447-3449 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The applicability of superconducting films in high-performance microwave devices suffers from inhomogeneous growth and local defects. Therefore we have installed a laser scanning system to visualize with spatial resolution the distribution of the microwave fields in 2-in.-diam YBaCuO disk resonators. The TM310 mode was imaged at a loaded quality factor of 8.3×104 via changes of the resonant frequency at 2.21 GHz and 40 K. The field distribution agreed with a magnetic-wall model, indicating at the contour of the disk fringe fields, but without strong edge enhancement. The data also indicated an inhomogeneous effective microwave penetration depth. The spatial resolution is presently limited to about 2 mm by heat diffusion. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122792
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  • 4
    Electronic Resource
    Electronic Resource
    High-quality Nb3Sn thin films on sapphire prepared by tin vapor diffusion (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 5021-5023 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stoichiometric Nb3Sn films on sapphire were prepared with a tin vapor diffusion process from sputtered Nb precursors. The superconductive properties of the precursor and the converted films were measured at 1 kHz and 87 GHz. The nanocrystalline Nb films yielded Tc=7.8–9.3 K, ΔTc=0.05–0.30 K, Jc (4.2 K)=0.8–2.8 MA/cm2, and ρ(Tc)=1–35 μΩ cm, indicating a high sensitivity to granularity and impurities. In contrast, the 0.5–3.0 μm thick and large-grained Nb3Sn films showed reproducibly Tc=18.0 K, ΔTc=0.1 K, Jc (4.2 K)=5–6.5 MA/cm2, and ρ(Tc)=7.7–9.1 μΩ cm. A reduced energy gap Δ/kTc=1.8–2.2 and a penetration depth λ0 (T=0 K)=65–80 nm were deduced from the surface impedance measurements. The residual surface resistance dropped below the sensitivity limit of 0.3 mΩ. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366372
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  • 5
    Electronic Resource
    Electronic Resource
    Pair and Quasiparticle States of YBa2Cu3O7−x Films Deduced from the Surface Impedance and a Comparison with Nb3Sn (1999)
    Springer
    Journal of superconductivity 12 (1999), S. 129-138 
    Details
    ISSN: 1572-9605
    Keywords: Surface impedance ; residual resistance ; energy gap ; two-band model ; magnetic scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Surface impedance data at 19 and 87 GHz of high-quality epitaxial YBCO films on different substrates are compared with data for Nb3Sn films on sapphire in terms of pair and quasiparticle (qp) transport. Surface resistance R s and penetration depth λ of YBCO are strongly affected by temperature dependent qp scattering, which is depressed in films with enhanced lattice strain. All films showed a comparable residual resistance R res(19 GHz)∼90 μΩ constituting a qp reservoir which is likely to be caused by the electronic configuration and by impurities. Subtracting R res from R s (T) revealed activated behavior with a reduced energy gap Δ0/k B T c∼0.9 for a film on sapphire, but power-law behavior for the other films. The penetration depth did not reveal power-law dependences at T≤0.5 ·T c, but was consistent with a reduced energy gap of 0.45 for a film on MgO. The increase of λ(T) at T≥0.5 · T c was related to qp scattering, which also caused an extremal conductivity σ1(T). A shoulder in λ(T) at T=(0.6–0.7) · T c confirmed evidence for the existence of two superconducting bands. The magnetic-field induced recovery of λ(B) of various YBCO films hinted for an important role of magnetic scattering. The results are in contradiction to a d-wave symmetry of the order parameter, at least for the chain band.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007750426204
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  • 6
    Electronic Resource
    Electronic Resource
    Experimental evaluation of the nonlinear surface resistance of YBa2Cu3O7−x step-edge grain boundary Josephson junctions (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 233-236 
    Details
    ISSN: 1572-9605
    Keywords: Microwave impedance ; microstrip resonator ; Josephson junction ; nonlinear power dissipation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The temperature, microwave current, and dc magnetic field dependencies of the effective surface resistanceR s of YBa2Cu3O7−x grain boundary Josephson junctions have been investigated at 6 GHz. The junctions were prepared on stepped LaAlO3 substrates and incorporated into tapered linear half-wavelength microstrip resonators. The characteristic parameters of the heterogeneous resonator were analyzed theoretically considering the junction as a lumped element of complex impedance. The microwave properties of the junction could then be extracted and related to their characteristic dc transport properties. The critical currentI c of the junction was found to limit the linear power dissipation in the superconducting strip. At microwave currents aboveI c , highly nonlinear microwave losses occurred, which displayed a characteristic magnetic field modulation. At even higher currents,R s saturated at a level corresponding to the normal resistanceR n of the junction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728308
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  • 7
    Electronic Resource
    Electronic Resource
    Two-gap structure in Yb(Y)Ba2Cu3O7−x single crystals (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 361-365 
    Details
    ISSN: 1572-9605
    Keywords: Tunneling spectroscopy ; high-T c superconductors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Tunneling effects in YbBa2Cu3O7−x (YbBCO) and YbBa2Cu3O7−x (YBCO) single crystals have been investigated using an improved technique of break junction preparation. A two-gap structure with BCS-like density of states has been observed. The value of the “large” gap is in the range of 24–28 meV for YBCO (T c =85–90 K) and 29–30 meV for YbBCO (T c =87–90 K). A variation of the value of the “small” gap between 0.5 and 11 meV has been detected, even for the same crystal. As a possible explanation, two-band superconductivity, surface properties, or strong gap anisotropy will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724569
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  • 8
    Electronic Resource
    Electronic Resource
    Nonlinear Power Handling of YBa2Cu3O7−x Films and Microwave Devices (1999)
    Springer
    Journal of superconductivity 12 (1999), S. 343-351 
    Details
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7−x ; power handling ; magnetic and thermal field limitations ; defects ; microwave quenches
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Physical mechanisms which limit the power handling of YBa2Cu3O7−x films and devices are discussed in terms of a quantitative classification scheme. The possible limitations are devided into magnetic or thermal, and global or local in nature. Analytical estimations are compared with measurements of YBa2Cu3O7−x films (Ø = 1″–2″) using a niobium-shielded sapphire resonator at 19 GHz, and disk resonators at 2 GHz. Magnetic effects are found to play an essential role in nonoptimized films in terms of weak-links, and in high-quality films if the lower critical field Bcl is reached. The majority of films and disk resonators appear to suffer from microwave heating. Global heating appears predominantly at CW operation. Local heating results mainly from defects in films of medium quality. Defect-induced quenches are observed at moderate field levels, sometimes resulting in an irreversible degradation of the power handling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007701332081
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  • 9
    Electronic Resource
    Electronic Resource
    Geometrical resonance effects in HTSC break junctions (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1225-1230 
    Details
    ISSN: 1573-7357
    Keywords: 74.50. +r ; 74.70. Vy ; 73.40. Gk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A periodic structure has been observed in the tunneling characteristics of HTSC break junctions. This structure is explained in terms of the electron-hole interference effect in the surface layer, which causes the formation of bound states in the normal regions N of the SNINS-type junctions. Good qualitative agreement has been found between experimental data and the predictions of the Arnolds proximity model. Several parameters of the SNINS-type structures have been derived from studies of Fiske resonances in HTSC Josephson break junctions in weak magnetic fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00753867
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